Charge/discharge control circuit and battery device

ABSTRACT

In order to provide a charge/discharge control circuit capable of controlling a charge/discharge current of secondary batteries that are connected in parallel, the charge/discharge control circuit includes: a first power supply terminal and a second power supply terminal to which a respective first electrode of each of secondary batteries which are connected in parallel is connected; a third power supply terminal to which second electrodes of the secondary batteries are connected; a connection circuit configured to connect the first power supply terminal and the second power supply terminal to generate an electric potential for an output; and a controller configured to operate on a potential difference between the electric potential supplied from the connection circuit and an electric potential supplied from the third power supply terminal, and to control charging/discharging of the first secondary battery and the second secondary battery.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to JapanesePatent Applications No. 2016-255308 filed on Dec. 28, 2016 and No.2017-125291 filed on Jun. 27, 2017, the entire content of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a charge/discharge control circuit anda battery device.

2. Description of the Related Art

Hitherto, there has been known a battery device that includes acharge/discharge control circuit (or a battery state monitoring circuit)having a controller (or a control circuit), and a plurality of secondarybatteries. The battery device described, for example, in Japanese PatentApplication Laid-open No. 2009-159811 uses the controller of thecharge/discharge control circuit to control a charge/discharge currentof the plurality of secondary batteries connected in series.

In the battery device described in Japanese Patent Application Laid-openNo. 2009-159811, the plurality of secondary batteries are connected inseries. However, parallel connection of the plurality of secondarybatteries can be instead thought of.

In the battery device described in Japanese Patent Application Laid-openNo. 2009-159811, the controller of the charge/discharge control circuitoperates on a charge/discharge current of the secondary batteries. Thecontroller of the charge/discharge control circuit may, however, losethe control of charging/discharging when an abnormality such as fall-offor an internal open-circuit failure of a secondary battery takes placein one of the plurality of secondary batteries because the plurality ofsecondary batteries are connected in series.

In the battery device described in Japanese Patent Application Laid-openNo. 2009-159811, an abnormality in one of the secondary batteries cutsoff the connection between the rest of the secondary batteries and anexternal terminal (output terminal). The loss of charge/dischargecontrol by the controller of the charge/discharge control circuittherefore does not particularly cause a problem.

In the case of parallel connection of the plurality of secondarybatteries, however, an abnormality in one of the secondary batteriesdoes not lead to the cutting off of the connection between the rest ofthe secondary batteries and an external terminal (output terminal). Theloss of charge/discharge control by the controller of thecharge/discharge control circuit in the case of parallel connection ofthe plurality of secondary batteries may accordingly render the batterydevice unstable when an abnormality occurs in one of the plurality ofsecondary batteries.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a charge/dischargecontrol circuit and a battery device in which a controller is capable ofcontrolling a charge/discharge current despite an abnormality in one ofa plurality of secondary batteries connected in parallel.

According to one embodiment of the present invention, there is provideda charge/discharge control circuit comprising: a first power supplyterminal to which a first electrode of a first secondary battery isconnected; a second power supply terminal to which a first electrode ofa second secondary battery is connected, the second secondary batterybeing connected in parallel to the first secondary battery; a thirdpower supply terminal to which second electrodes of the first secondarybattery and the second secondary battery are connected; a connectioncircuit configured to connect the first power supply terminal and thesecond power supply terminal, and to output an electric potential thatis generated after the connection; and a controller configured tooperate on a power supply voltage that is a potential difference betweenthe electric potential output from the connection circuit and anelectric potential supplied from the third power supply terminal, and tocontrol charging/discharging of the first secondary battery and thesecond secondary battery.

According to the charge/discharge control circuit of the presentinvention, the controller is capable of controlling a charge/dischargecurrent despite an abnormality in one of the plurality of secondarybatteries connected in parallel sine the connection circuit is includedbetween the controller and the power supply terminals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for illustrating a functional configuration of abattery device to which a charge/discharge control circuit according tothe first embodiment of the present invention is applied.

FIG. 2 is a diagram for illustrating a functional configuration of abattery device to which a charge/discharge control circuit according tothe second embodiment of the present invention is applied.

FIG. 3 is a diagram for illustrating a functional configuration of abattery device to which a charge/discharge control circuit according tothe third embodiment of the present invention is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Referring to the accompanying drawings, a charge/discharge controlcircuit 10 according to the first embodiment of the present invention isdescribed below.

FIG. 1 is a diagram for illustrating the function configuration of abattery device 1 to which the charge/discharge control circuit 10according to the first embodiment is applied.

The battery device 1 includes the charge/discharge control circuit 10, afirst secondary battery B1, a second secondary battery B2, a firstexternal terminal EB+, a second external terminal EB−, a dischargecontrol switch SD1, a charge control switch SC1, a discharge controlswitch SD2, a charge control switch SC2, and a resistor R.

The first secondary battery B1 and the second secondary battery B2 forma secondary battery B. The first secondary battery B1 includes a firstelectrode B11 and a second electrode B12. The second secondary batteryB2 includes a first electrode B21 and a second electrode B22.

The first external terminal EB+ and the second external terminal EB−form an external terminal EB.

The discharge control switch SD1 and the charge control switch SC1 forma first charge/discharge control switch. The discharge control switchSD2 and the charge control switch SC2 form a second charge/dischargecontrol switch.

The battery device 1 is configured to supply power that is charged inthe secondary battery B to the outside via the external terminal EB, andto charge the secondary battery B with power supplied from the outsidevia the external terminal EB. The battery device 1 includes thesecondary battery B having a necessary number of parallel connections.

The charge/discharge control circuit 10 includes a first power supplyterminal VSS1, a second power supply terminal VSS2, a third power supplyterminal VDD, a discharge control terminal DO, a charge control terminalCO, an overcurrent detection terminal VM, a first voltage detector 111,a second voltage detector 112, a connection circuit 14, a controller 12,and a driver 13.

The first voltage detector 111 and the second voltage detector 112 forma voltage detector 11. The connection circuit 14 includes a firstresistor 141 and a second resistor 142. The first resistor 141 includesa first terminal 141 a and a second terminal 141 b. The second resistor142 includes a first terminal 142 a and a second terminal 142 b.

The first external terminal EB+ is connected to the second electrode B12of the first secondary battery B1, the second electrode B22 of thesecond secondary battery B2, and the third power supply terminal VDD ofthe charge/discharge control circuit 10. The first electrode B11 of thefirst secondary battery B1 is connected to the first power supplyterminal VSS1 of the charge/discharge control circuit 10 and oneterminal of the discharge control switch SD1. The first electrode B21 ofthe secondary battery B2 is connected to the second power supplyterminal VSS2 of the charge/discharge control circuit 10 and oneterminal of the discharge control switch SD2. The other terminal of thedischarge control switch SD1 is connected to one terminal of the chargecontrol switch SC1, and a signal from the discharge control terminal DOis used to control the discharge control switch SD1. The other terminalof the discharge control switch SD2 is connected to one terminal of thecharge control switch SC2, and a signal from the discharge controlterminal DO is used to control the discharge control switch SD2. Theother terminal of the charge control switch SC1 is connected to thesecond external terminal EB−, and a signal from the charge controlterminal CO is used to control the charge control switch SC1. The otherterminal of the charge control switch SC2 is connected to the secondexternal terminal EB−, and a signal from the charge control terminal COis used to control the charge control switch SC2. The overcurrentdetection terminal VM is connected to the second external terminal EB−via the resistor R.

The first voltage detector 111 is connected to the first power supplyterminal VSS1, the third power supply terminal VDD, the overcurrentdetection terminal VM, and the controller 12. The second voltagedetector 112 is connected to the second power supply terminal VSS2, thethird power supply terminal VDD, the overcurrent detection terminal VM,and the controller 12. In the first resistor 141 of the connectioncircuit 14, the first terminal 141 a is connected to the first powersupply terminal VSS1 and the second terminal 141 b is connected to thecontroller 12. In the second resistor 142 of the connection circuit 14,the first terminal 142 a is connected to the second power supplyterminal VSS2 and the second terminal 142 b is connected to thecontroller 12. The controller 12 is connected to the driver 13. Thedriver 13 is connected to the discharge control terminal DO and thecharge control terminal CO.

The first voltage detector 111 is configured to detect the voltage ofthe first secondary battery B1 based on the electric potential of thefirst power supply terminal VSS1 and the electric potential of the thirdpower supply terminal VDD. The first voltage detector 111 in the exampleof FIG. 1 also detects an overcurrent flowing in the firstcharge/discharge control switch, based on a voltage applied between thefirst power supply terminal VSS1 and the overcurrent detection terminalVM.

The second voltage detector 112 is configured to detect the voltage ofthe second secondary battery B2 based on the electric potential of thesecond power supply terminal VSS2 and the electric potential of thethird power supply terminal VDD. The second voltage detector 112 in theexample of FIG. 1 also detects an overcurrent flowing in the secondcharge/discharge control switch, based on a voltage applied between thesecond power supply terminal VSS2 and the overcurrent detection terminalVM.

The connection circuit 14 is configured to connect the first powersupply terminal VSS1 and the second power supply terminal VSS2 to eachother via the first resistor 141 and the second resistor 142, and tooutput to the controller 12 an electric potential that is generatedafter the connection.

The controller 12 is configured to output a signal that is used tocontrol a charge/discharge current to/from the first secondary batteryB1 and the second secondary battery B2, based on the result of detectionby the first voltage detector 111 and the result of detection by thesecond voltage detector 112. The controller 12 operates on a powersupply voltage that is a potential difference between the electricpotential output from the connection circuit 14 and the electricpotential supplied from the third power supply terminal VDD.

The driver 13 is configured to output, from the charge control terminalCO, a signal that is used to control the charge control switch SC1 andthe charge control switch SC2, and, from the discharge control terminalDO, a signal that is used to control the discharge control switch SD1and the discharge control switch SD2, based on a signal output by thecontroller 12.

The charge control switch SC1 is configured to control a charge currentfor charging the first secondary battery B1. The charge control switchSC2 is configured to control a charge current for charging the secondsecondary battery B2. The discharge control switch SD1 is configured tocontrol a discharge current that is discharged by the first secondarybattery B1. The discharge control switch SD2 is configured to control adischarge current that is discharged by the second secondary battery B2.

In the following description, the switches may collectively be referredto as “control switches”. The charge control switch SC1 and the chargecontrol switch SC2 may collectively be referred to as “charge controlswitches”. The discharge control switch SD1 and the discharge controlswitch SD2 may collectively be referred to as “discharge controlswitches”.

Every one of the control switches is, for example, an FET switch, and isswitched on or off under control of the charge/discharge control circuit10.

The controller 12 controls the charging/discharging of the secondarybatteries B by controlling the control switches via the driver 13 basedon the result of detection that is performed by the voltage detector 11.

An example of control exerted by the controller 12 is described below.

The controller 12 controls the control switches so that each controlswitch is switched on when the detection result of the voltage detector11 indicates a “normal state”.

When the detection result of the first voltage detector 111 indicates“overcharging”, that is, when the first secondary battery B1 isovercharged, the controller 12 controls the charge control switches tobe off, cutting off a charge current to the secondary battery B to stopthe charging.

When the detection result of the first voltage detector 111 indicates“overdischarging”, that is, when the first secondary battery B1 isoverdischarged, the controller 12 controls the discharge controlswitches to be off, cutting off a discharge current from the secondarybattery B to stop the discharging.

When the detection result of the second voltage detector 112 indicates“overcharging”, that is, when the second secondary battery B2 isovercharged, the controller 12 controls the charge control switches tobe off, cutting off a charge current to the secondary battery B to stopthe charging.

When the detection result of the second voltage detector 112 indicates“overdischarging”, that is, when the second secondary battery B2 isoverdischarged, the controller 12 controls the discharge controlswitches to be off, cutting off a discharge current from the secondarybattery B to stop the discharging.

A case is described in which a failure in the battery device 1 makes itimpossible to supply an electric potential to one of the first powersupply terminal VSS1 and the second power supply terminal VSS2.

The description takes as an example a case in which an electricpotential can no longer be supplied to the second power supply terminalVSS2 due to the breaking of a conductive wire connected to the firstelectrode B21 of the second secondary battery B2.

The electric potential of the first electrode B21 in the secondsecondary cell B2 is not supplied to the second power supply terminalVSS2 of the charge/discharge control circuit 10. The connection circuit14 deals with this by outputting the electric potential of the firstpower supply terminal VSS1. The controller 12 consequently operates on apower supply voltage that is a potential difference between the electricpotential of the third power supply terminal VDD and the electricpotential of the first power supply terminal VSS1.

In other words, the charge/discharge control circuit 10, which includesthe connection circuit 14, is capable of running the controller 12 evenwhen no electric potential is supplied from one of the first powersupply terminal VSS1 and the second power supply terminal VSS2.

The controller 12 can also operate despite an abnormality in the secondsecondary battery B2, for example, the falling off of or an internalopen circuit failure in the second secondary battery B2 because thefirst secondary battery B1 supplies a power supply voltage to thecontroller 12 in that event.

Similarly, the controller 12 can operate on a power supply voltage thatis supplied by the second secondary battery B2 when a conductive wire ofthe first secondary battery B1 breaks, or when there is an abnormalityin the first secondary battery B1, for example, the falling off of or aninternal open circuit failure in the first secondary battery B1.

As described above, even when an output wire from one of a plurality ofsecondary batteries connected in parallel breaks, the battery device 1according to the first embodiment is capable of charging/discharging andmonitoring another of the plurality of secondary batteries.

When the first secondary battery B1, for example, short-circuitsinternally, a large current accidentally flows into the second secondarybattery B2 via the first secondary battery B1 and the control switchesor the connection circuit 14.

In this case, the resistance value of the connection circuit 14 is setto a resistance value that is higher than the ON resistance value of thecontrol switches and high enough to satisfactorily limit the amount ofcurrent that flows via the connection circuit 14. This causes most ofthe current to flow via the control switches. In addition, the highresistance value keeps satisfactorily limiting the amount of currentflowing in the connection circuit 14 after the charge/discharge controlcircuit 10 detects the overcurrent and switches off the charge switches,thereby preventing damage to the charge/discharge control circuit 10.

Damage to the charge/discharge control circuit 10 is similarly preventedwhen the second secondary battery B2 short-circuits internally.

Another effect is that the voltage of the first secondary battery B1 andthe voltage of the second secondary battery B2 can be balanced becausethe first secondary battery B1 and the second secondary battery B2 areconnected to each other via the first resistor 141 and the secondresistor 142 even when, for example, the discharge control switches areswitched off in an over-discharge state.

Second Embodiment

A charge/discharge control circuit 10 according to the second embodimentof the present invention is described below. The charge/dischargecontrol circuit 10 according to the second embodiment is configuredsimilarly to the charge/discharge control circuit 10 according to thefirst embodiment, except for points described later. Descriptions oncomponents that are the same as those of the charge/discharge controlcircuit 10 according to the first embodiment are thus omitted.

FIG. 2 is a diagram for illustrating the function configuration of abattery device 1 to which the charge/discharge control circuit 10according to the second embodiment is applied.

The connection circuit 14 includes a first diode 143 and a second diode144. The first diode 143 includes a cathode terminal 143 a and an anodeterminal 143 b. The second diode 144 includes a cathode terminal 144 aand an anode terminal 144 b. In the first diode 143, the cathodeterminal 143 a is connected to the first power supply terminal VSS1 andthe anode terminal 143 b is connected to the controller 12. In thesecond diode 144, the cathode terminal 144 a is connected to the secondpower supply terminal VSS2 and the anode terminal 144 b is connected tothe controller 12.

With the connection circuit 14 configured as above, the battery device 1according to the second embodiment is capable of, even when an outputwire from one of a plurality of secondary batteries connected inparallel breaks, charging/discharging and monitoring another of theplurality of secondary batteries as in the first embodiment.

The charge/discharge control circuit 10 is also free from damage whenone of the first secondary battery B1 and the second secondary batteryB2 short-circuits internally, because a current does not flow from theshort-circuited secondary battery B via the connection circuit 14.

Third Embodiment

A charge/discharge control circuit 10 according to the third embodimentof the present invention is described below. The charge/dischargecontrol circuit 10 according to the third embodiment is configuredsimilarly to the charge/discharge control circuit 10 according to thefirst embodiment, except for points described later. Descriptions oncomponents that are the same as those of the charge/discharge controlcircuit 10 according to the first embodiment are thus omitted.

FIG. 3 is a diagram for illustrating the function configuration of abattery device 1 to which the charge/discharge control circuit 10according to the third embodiment is applied.

The connection circuit 14 includes a first constant current diode 145and a second constant current diode 146. The first constant currentdiode 145 includes an anode terminal 145 a and a cathode terminal 145 b.The second constant current diode 146 includes an anode terminal 146 aand a cathode terminal 146 b. In the first constant current diode 145,the anode terminal 145 a is connected to the first power supply terminalVSS1 and the cathode terminal 145 b is connected to the controller 12.In the second constant current diode 146, the anode terminal 146 a isconnected to the second power supply terminal VSS2 and the cathodeterminal 146 b is connected to the controller 12.

With the connection circuit 14 configured as above, the battery device 1according to the third embodiment is capable of, even when an outputwire from one of a plurality of secondary batteries connected inparallel breaks, charging/discharging and monitoring another of theplurality of secondary batteries as in the first embodiment.

When an internal short-circuit occurs in the first secondary battery B1,for example, the amount of current flowing in the connection circuit 14is limited by a pinch-off voltage of the first constant current diode145. Damage to the charge/discharge control circuit 10 is thus preventedby setting the pinch-off voltage to an appropriate value. Damage to thecharge/discharge control circuit 10 is similarly avoided when the secondsecondary battery B2 short-circuits internally.

Another effect is that the voltage of the first secondary battery B1 andthe voltage of the second secondary battery B2 can be balanced as in thefirst embodiment, because the first secondary battery B1 and the secondsecondary battery B2 are connected to each other via the first constantcurrent diode 145 and the second constant current diode 146 even whenthe discharge control switches are switched off in an over-dischargestate.

This concludes the descriptions on the embodiments of the presentinvention. The present invention is not limited to the configurations ofthe embodiments, and is receptive of omission, substitution, andmodification in various manners without departure from the spirit of thepresent invention. For example, while the battery devices described inthe embodiments each have charge/discharge switches on the negativeelectrode side of the secondary batteries and give the secondarybatteries a common positive electrode, the battery device may insteadhave charge/discharge switches on the positive electrode side of thesecondary batteries and give the secondary batteries a common negativeelectrode. To give another example, the discharge control switch SD1 andthe discharge control switch SD2, which are configured to have commoncontrol, and the charge control switch SC1 and the charge control switchSC2, which are configured to have common control, may have a circuitconfiguration designed so that each control switch is controlledindividually.

What is claimed is:
 1. A charge/discharge control circuit configured tocontrol charging/discharging of a first secondary battery and a secondsecondary battery which are connected in parallel to each other betweena first external terminal and a second external terminal, thecharge/discharge control circuit comprising: a first power supplyterminal to which a first electrode of the first secondary battery isconnected; a second power supply terminal to which a first electrode ofthe second secondary battery is connected; a third power supply terminalto which a second electrode of the first secondary battery and a secondelectrode of the second secondary battery are connected; a first voltagedetector configured to detect a voltage of the first secondary batterybased on an electric potential of the first power supply terminal and anelectric potential of the third power supply terminal; a second voltagedetector configured to detect a voltage of the second secondary batterybased on an electric potential of the second power supply terminal andthe electric potential of the third power supply terminal; a connectioncircuit configured to connect the first power supply terminal and thesecond power supply terminal to generate an electric potential for anoutput; and a controller configured to operate on a power supply voltagethat is a potential difference between the electric potential outputfrom the connection circuit and the electric potential supplied from thethird power supply terminal, and to control charging/discharging of thefirst secondary battery and the second secondary battery based on aresult of detection by the first voltage detector and a result ofdetection by the second voltage detector.
 2. The charge/dischargecontrol circuit according to claim 1, wherein the connection circuitcomprises: a first resistor including a first terminal connected to thefirst power supply terminal and a second terminal connected to thecontroller; and a second resistor including a first terminal connectedto the second power supply terminal and a second terminal connected tothe controller.
 3. The charge/discharge control circuit according toclaim 1, wherein the connection circuit comprises: a first diodeincluding a cathode terminal connected to the first power supplyterminal and an anode terminal connected to the controller; and a seconddiode including a cathode terminal connected to the second power supplyterminal and an anode terminal connected to the controller.
 4. Thecharge/discharge control circuit according to claim 1, wherein theconnection circuit comprises: a first constant current diode includingan anode terminal connected to the first power supply terminal and acathode terminal connected to the controller; and a second constantcurrent diode including an anode terminal connected to the second powersupply terminal and a cathode terminal connected to the controller.
 5. Abattery device, comprising: the charge/discharge control circuit ofclaim 1; the first secondary battery; the second secondary battery; thefirst external terminal; the second external terminal; a firstcharge/discharge control switch controlled by the controller andconfigured to control a charge/discharge current to/from the firstsecondary battery; and a second charge/discharge control switchcontrolled by the controller and configured to control acharge/discharge current to/from the second secondary battery.
 6. Abattery device, comprising: the charge/discharge control circuit ofclaim 2; the first secondary battery; the second secondary battery; thefirst external terminal; the second external terminal; a firstcharge/discharge control switch controlled by the controller andconfigured to control a charge/discharge current to/from the firstsecondary battery; and a second charge/discharge control switchcontrolled by the controller and configured to control acharge/discharge current to/from the second secondary battery.
 7. Abattery device, comprising: the charge/discharge control circuit ofclaim 3; the first secondary battery; the second secondary battery; thefirst external terminal; the second external terminal; a firstcharge/discharge control switch controlled by the controller andconfigured to control a charge/discharge current to/from the firstsecondary battery; and a second charge/discharge control switchcontrolled by the controller and configured to control acharge/discharge current to/from the second secondary battery.
 8. Abattery device, comprising: the charge/discharge control circuit ofclaim 4; the first secondary battery; the second secondary battery; thefirst external terminal; the second external terminal; a firstcharge/discharge control switch controlled by the controller andconfigured to control a charge/discharge current to/from the firstsecondary battery; and a second charge/discharge control switchcontrolled by the controller and configured to control acharge/discharge current to/from the second secondary battery.